PG 1018−047 : the longest period subdwarf B binary

About 50 per cent of all known hot subdwarf B stars (sdBs) reside in close (short-period) binaries, for which common-envelope ejection is the most likely formation mechanism. However, Han et al. predict that the majority of sdBs should form through stable mass transfer leading to long-period binaries. Determining orbital periods for these systems is challenging and while the orbital periods of ∼100 short-period systems have been measured, there are no periods measured above 30 d. As part of a large programme to characterize the orbital periods of sdB binaries and their formation history, we have found that PG 1018−047 has an orbital period of 759.8 ± 5.8 d, easily making it the longest period ever detected for a sdB binary. Exploiting the Balmer lines of the subdwarf primary and the narrow absorption lines of the companion present in the spectra, we derive the radial velocity amplitudes of both stars, and estimate the mass ratio MMS/MsdB= 1.6 ± 0.2. From the combination of visual and infrared photometry, the spectral type of the companion star is determined to be mid-K

Evolutionary constraints on the long-period subdwarf B binary PG1018-047

We have revisited the sdB+K-star long-period binary PG 1018–047 based on 20 new high-resolution Very Large Telescope/Ultraviolet and Visual Echelle Spectrograph spectra that provided regular coverage over a period of more than 26  m. We refine the period and establish that the orbit is significantly eccentric (P = 751.6 ± 1.9 d and e = 0.049 ± 0.008). A simultaneous fit derived from the narrow metal lines visible in the spectrum of the sdB star and the metal lines in the red part of the spectrum that originate from the companion provides the mass ratio, MMS/MsdB = 1.52 ± 0.04, for the system. From an NLTE model atmosphere analysis of the combined spectra, we find Teff = 29900 ± 330 K, log g = 5.65 ± 0.06 dex and log(nHe/nH) = –3.98 ± 0.16 dex for the primary, consistent with a B-type hot subdwarf star. The spectral contribution of the companion is consistent with a K5V-type star. With the companion having a mass of only ∼ 0.7 M⊙, this system lies close to the boundary below which stable Roche lobe overflow (RLOF) cannot be supported. To model the evolution of such a system, we have extended earlier MESA models towards lower companion masses. We find that both phase-dependent mass loss during RLOF, when 30 to 40 per cent of the available mass is lost through the outer Lagrange point and phase-dependent mass loss during RLOF in combination with a circumbinary disc of maximum MCB = 0.001 M⊙ could have formed the PG 1018–047 binary system

Investigating Mercury's Environment with the Two-Spacecraft BepiColombo Mission

The ESA-JAXA BepiColombo mission will provide simultaneous measurements from two spacecraft, offering an unprecedented opportunity to investigate magnetospheric and exospheric dynamics at Mercury as well as their interactions with the solar wind, radiation, and interplanetary dust. Many scientific instruments onboard the two spacecraft will be completely, or partially devoted to study the near-space environment of Mercury as well as the complex processes that govern it. Many issues remain unsolved even after the MESSENGER mission that ended in 2015. The specific orbits of the two spacecraft, MPO and Mio, and the comprehensive scientific payload allow a wider range of scientific questions to be addressed than those that could be achieved by the individual instruments acting alone, or by previous missions. These joint observations are of key importance because many phenomena in Mercury's environment are highly temporally and spatially variable. Examples of possible coordinated observations are described in this article, analysing the required geometrical conditions, pointing, resolutions and operation timing of different BepiColombo instruments sensors.Peer reviewe

Magnetic reconnection driven by electron dynamics

Magnetic reconnections play essential roles in space, astrophysical, and laboratory plasmas, where the anti-parallel magnetic field components re-connect and the magnetic energy is converted to the plasma energy as Alfvénic out flows. Although the electron dynamics is considered to be essential, it is highly challenging to observe electron scale reconnections. Here we show the experimental results on an electron scale reconnection driven by the electron dynamics in laser-produced plasmas. We apply a weak-external magnetic field in the direction perpendicular to the plasma propagation, where the magnetic field is directly coupled with only the electrons but not for the ions. Since the kinetic pressure of plasma is much larger than the magnetic pressure, the magnetic field is distorted and locally anti-parallel. We observe plasma collimations, cusp and plasmoid like features with optical diagnostics. The plasmoid propagates at the electron Alfvén velocity, indicating a reconnection driven by the electron dynamics

Investigating Mercury's Environment with the Two-Spacecraft BepiColombo Mission

The ESA-JAXA BepiColombo mission will provide simultaneous measurements from two spacecraft, offering an unprecedented opportunity to investigate magnetospheric and exospheric dynamics at Mercury as well as their interactions with the solar wind, radiation, and interplanetary dust. Many scientific instruments onboard the two spacecraft will be completely, or partially devoted to study the near-space environment of Mercury as well as the complex processes that govern it. Many issues remain unsolved even after the MESSENGER mission that ended in 2015. The specific orbits of the two spacecraft, MPO and Mio, and the comprehensive scientific payload allow a wider range of scientific questions to be addressed than those that could be achieved by the individual instruments acting alone, or by previous missions. These joint observations are of key importance because many phenomena in Mercury's environment are highly temporally and spatially variable. Examples of possible coordinated observations are described in this article, analysing the required geometrical conditions, pointing, resolutions and operation timing of different BepiColombo instruments sensors

Electrostatic Dust Analyzer (EDA) for Characterizing Dust Transport on the Lunar Surface

International audienceElectrostatic dust charging and transport is a five-decade-old problem related to a number of observations on the surfaces of the Moon and other airless bodies, including the lunar horizon glow, the dust ponds on asteroid Eros and comet 67P, and the radial spokes in Saturn's rings. Recent laboratory studies have made important breakthroughs in understanding the fundamentals of dust charging, mobilization and lofting mechanisms, offering strong support for its occurrence on the surfaces of airless bodies including the Moon. However, there are currently no unambiguous measurements that can confirm this electrostatic phenomenon in space. Currently, an Electrostatic Dust Analyzer (EDA) is under development through NASA's DALI program for future lunar landed missions in order to determine ground truth about this phenomenon. EDA measures the charge, mass and velocity of lofted dust particles on the lunar surface. The instrument consists of two identical Dust Trajectory Sensors (DTS) each on one end of the instrument and a Deflection Field Electrodes (DFE) unit lying in between the two DTS. The charge and velocity of a dust particle entering the instrument are measured from image charges induced on the wire electrodes in the DTS. The mass of the dust particle is derived from its deflected trajectory by the DFE. Importantly, the EDA measurements will determine the lofting rate that helps us understand how fast this process goes against other surface processes such as space weathering. Measurements enabled by EDA will improve our understanding of the role of electrostatic dust transport in shaping the surface physical properties and near-surface dust environment on the Moon, as well as make important implications to such a surface process on other airless bodies, including Near-Earth-Asteroids (NEAs) and Maritain moons. Additionally, these measurements will help understand potential dust hazards to future robotic and human exploration on the lunar surface

Electrostatic Dust Analyzer (EDA) for Characterizing Dust Transport on the Lunar Surface

International audienceElectrostatic dust charging and transport is a five-decade-old problem related to a number of observations on the surfaces of the Moon and other airless bodies, including the lunar horizon glow, the dust ponds on asteroid Eros and comet 67P, and the radial spokes in Saturn's rings. Recent laboratory studies have made important breakthroughs in understanding the fundamentals of dust charging, mobilization and lofting mechanisms, offering strong support for its occurrence on the surfaces of airless bodies including the Moon. However, there are currently no unambiguous measurements that can confirm this electrostatic phenomenon in space. Currently, an Electrostatic Dust Analyzer (EDA) is under development through NASA's DALI program for future lunar landed missions in order to determine ground truth about this phenomenon. EDA measures the charge, mass and velocity of lofted dust particles on the lunar surface. The instrument consists of two identical Dust Trajectory Sensors (DTS) each on one end of the instrument and a Deflection Field Electrodes (DFE) unit lying in between the two DTS. The charge and velocity of a dust particle entering the instrument are measured from image charges induced on the wire electrodes in the DTS. The mass of the dust particle is derived from its deflected trajectory by the DFE. Importantly, the EDA measurements will determine the lofting rate that helps us understand how fast this process goes against other surface processes such as space weathering. Measurements enabled by EDA will improve our understanding of the role of electrostatic dust transport in shaping the surface physical properties and near-surface dust environment on the Moon, as well as make important implications to such a surface process on other airless bodies, including Near-Earth-Asteroids (NEAs) and Maritain moons. Additionally, these measurements will help understand potential dust hazards to future robotic and human exploration on the lunar surface

Electrostatic Dust Analyzer (EDA) for Characterizing Dust Transport on the Lunar Surface

International audienceElectrostatic dust charging and transport is a five-decade-old problem related to a number of observations on the surfaces of the Moon and other airless bodies, including the lunar horizon glow, the dust ponds on asteroid Eros and comet 67P, and the radial spokes in Saturn's rings. Recent laboratory studies have made important breakthroughs in understanding the fundamentals of dust charging, mobilization and lofting mechanisms, offering strong support for its occurrence on the surfaces of airless bodies including the Moon. However, there are currently no unambiguous measurements that can confirm this electrostatic phenomenon in space. Currently, an Electrostatic Dust Analyzer (EDA) is under development through NASA's DALI program for future lunar landed missions in order to determine ground truth about this phenomenon. EDA measures the charge, mass and velocity of lofted dust particles on the lunar surface. The instrument consists of two identical Dust Trajectory Sensors (DTS) each on one end of the instrument and a Deflection Field Electrodes (DFE) unit lying in between the two DTS. The charge and velocity of a dust particle entering the instrument are measured from image charges induced on the wire electrodes in the DTS. The mass of the dust particle is derived from its deflected trajectory by the DFE. Importantly, the EDA measurements will determine the lofting rate that helps us understand how fast this process goes against other surface processes such as space weathering. Measurements enabled by EDA will improve our understanding of the role of electrostatic dust transport in shaping the surface physical properties and near-surface dust environment on the Moon, as well as make important implications to such a surface process on other airless bodies, including Near-Earth-Asteroids (NEAs) and Maritain moons. Additionally, these measurements will help understand potential dust hazards to future robotic and human exploration on the lunar surface

Electrostatic Dust Analyzer (EDA) for Characterizing Dust Transport on the Lunar Surface

International audienceElectrostatic dust charging and transport is a five-decade-old problem related to a number of observations on the surfaces of the Moon and other airless bodies, including the lunar horizon glow, the dust ponds on asteroid Eros and comet 67P, and the radial spokes in Saturn's rings. Recent laboratory studies have made important breakthroughs in understanding the fundamentals of dust charging, mobilization and lofting mechanisms, offering strong support for its occurrence on the surfaces of airless bodies including the Moon. However, there are currently no unambiguous measurements that can confirm this electrostatic phenomenon in space. Currently, an Electrostatic Dust Analyzer (EDA) is under development through NASA's DALI program for future lunar landed missions in order to determine ground truth about this phenomenon. EDA measures the charge, mass and velocity of lofted dust particles on the lunar surface. The instrument consists of two identical Dust Trajectory Sensors (DTS) each on one end of the instrument and a Deflection Field Electrodes (DFE) unit lying in between the two DTS. The charge and velocity of a dust particle entering the instrument are measured from image charges induced on the wire electrodes in the DTS. The mass of the dust particle is derived from its deflected trajectory by the DFE. Importantly, the EDA measurements will determine the lofting rate that helps us understand how fast this process goes against other surface processes such as space weathering. Measurements enabled by EDA will improve our understanding of the role of electrostatic dust transport in shaping the surface physical properties and near-surface dust environment on the Moon, as well as make important implications to such a surface process on other airless bodies, including Near-Earth-Asteroids (NEAs) and Maritain moons. Additionally, these measurements will help understand potential dust hazards to future robotic and human exploration on the lunar surface